Detonation measurements using single optical fibers

Classical physics of detonation assumes the basic configuration of Chapman-Jouguet mechanisms with an interaction between shock and reaction zones. The Chapman-Jouguet one-dimensional regime (CJ point) obeys to the assumption of the entire flow to be one-dimensional and the front is assumed as a non thickness discontinuity plane, where conservation laws for shock waves (mass, momentum and energy) are applied. This last assumption simplifies detonation measurements implying, as basic values, detonation velocity and pressure. Radiation assumptions and measurements, coupled with described analytical model, led to develop a multi-channel optical analyzer - multi-fiber optical probes (MFOP). Despite the last fifteen years passed, since MFOP was developed, it remains, up to the present, a very complex diagnostic technique that offers a complex compromise between high temporal/spatial resolutions. However, their design stays complex and a fast streak camera is always a condition to record the results. Also the triggering mechanisms and sweep time evaluations stay as delicate operations. These conclusions lead us to develop a more simplified method, based in single optical fibers and fast optical/electric sensors connected to a digital signal analyzer. Two kinds of optical multimode fibers can be used in these measurements: PMMA and silica fibers. In a similar way, two kinds of opto-electronic receivers can be used, as a function of optical range: maximum sensibility at 650 and 850 nm. Sensors were selected to have rise time less than 50 ns. Opto-electronic converters were designed and built. Best results were achieved for PMMA multimode optic fiber, connected to an analog 650 nm receiver. The used tested explosive was a PETN detonating cord. Records were obtained and an example of detonation velocity measurement is shown. Results show promising possibilities. More complex configurations and results, coupling preceding methods and results, will be tested in future. Obtained results prove the validity of presented experimental method.